Known in the art are flow meters (GB, B, 1109592) comprising a pair of rotors which rotate synchronously with a roller installed in a spaced relation to, and in a casing having ports for fluid admission and discharge. Surfaces of the casing, rotors and roller define a working space which is of an intricate configuration. These flow meters have a complicated kinematic system, and their casing is very hard to make; it is difficult to determine exactly the working volume of the flow meter and it is hardly possible to manufacture small-size flow meters of this type.
The provision of the two rotors results in an increased load imposed on a synchronizing device which is generally built around gears thus leading to an increase in a pressure differential across the flow meter and to a rapid wear of the synchronizing gears. All these factors limit the range of measurement within which flow can be determined with a high accuracy.
Known in the art is a flow meter (SU, A, 246100) comprising a rotor having vanes which is mounted with sealing gaps in a casing and defines a working space in the casing. The casing has ports for admission and discharge of fluid and recesses accommodating rollers which are mounted in a spaced relation thereto and which divide the working space into a fluid admission chamber and a fluid discharge chamber. The rollers have grooves for the rotor vanes to pass there-through, and the rotor is mounted for rotation in synchronism with the rollers under the action of fluid energy.
Roller rotation occurs under the conditions of a substantial viscous friction in clearances defined between the surfaces of the recesses and rollers. The friction in the clearances causes a substantial pressure differential in the working space which limits the flow measurement range.
The value of friction in the clearances, hence, pressure differential in the working space depends not only on the clearance length, but also on the clearance value .delta. which is not pre-set in this flow meter. In addition, leakages, hence accuracy of flow measurements also depend on the clearance value.